Tapjoy's research which reaches over 200 million iOS users a month shows that iOS 8 adoption is significantly slower than iOS 7. After 18 hours available iOS 8 is at a 6% adoption rate, compared to iOS 7, which was at 12%. According to their data, 6.6% of iPhone owners are using iOS 8, compared to 7.6% of iPod and 3.9% of iPad owners.
A quick look at the numbers tells an interesting story. For instance, while it took approximately seven hours for iOS 7 to reach 10% adoption, which was twice as fast as it took iOS 6 to reach that level of penetration, iOS 8 stands at under 6% eighteen hours after its initial availability, while iOS 7 was at 12% after the same time period.
Mixpanel on the other hand has current usage rates at iOS 8 14.75% and iOS 7 at 81.6%.Finally, Fiksu has a graph that shows 'hours since release.' Relative to prior iOS launches, iOS 8 reached 9.48% adoption, while iOS 7 was at 19.4% and iOS 6 was at 12.42%. All these percentages are iOS adoption rates 21 hours from their initial release.
There could be a number of reasons why iOS 8 has seen slower adoption rates. iOS 7 was filled with hype by consumers as it brought an entire new look and feel for the first time to iOS. In addition, iOS 8 requires up to 6GB of free space to install the update OTA, which could cause some people to hold off on an update.